1. Field of the Invention
The present invention relates to a method for making connections for conference calls, and more particularly to such a method used in connection with a PCM time division multiplex switching system for a communications network.
2. The Prior Art
Communication systems including pulse code modulation (PCM) time division multiplex switching employ systems which define sequential pulse frames, each of which are subdivided into a plurality of time slots. Each of the time slots is devoted to an individual communication unit, such as a telephone line or other transmission line. The amplitude of a signal on the line is sampled during its respective time slot, and a digital representation of this amplitude is made available to one or more other lines, during the time slots allocated to them. Sampling of the individual transmission lines, during their respective time slots, produces digital code words, which are handled by digital processing apparatus with great speed. Conference calls are handled in some existing systems by summing a plurality of message samples and reading out the sums to the conference participants. Such systems have not provided, however, for conference calls involving subscribers having adjacent time slots.